In the process of manufacturing a silicon microchip, light is directed through a reticle mask to etch circuits into a silicon wafer disc. The presence of dirt, dust, smudges, scratches or other flaws on the surface of the silicon wafer is highly undesirable and will adversely affect the resulting circuits. As a result, the silicon wafers are necessarily inspected prior to and during the manufacturing process. One common inspection technique is for a human inspector to visually examine the surface under intense light and magnification. However, the microscope has a small field of view so it takes a human inspector an extended period of time to visually examine the entire surface of the wafer.
Laser surface inspection devices have been developed for inspecting the surface of polished silicon wafers to accurately detect small particles or flaws. Examples of such devices are disclosed in Alford et al. U.S. Pat. No. 4,376,583 issued Mar. 15, 1983 and Moran U.S. Pat. No. 4,630,276 issued Dec. 16, 1986. In these known laser surface inspection systems, a laser beam is traversed across the surface of the silicon wafer and the reflections from the wafer are collected and analyzed to provide information about any flaws present on the wafer surface. The light is specularly reflected from the polished surface of the wafer, but in locations where the beam strikes surface flaws, the light is scattered. By separately collecting the scattered and specularly reflected light, the inspection device can quickly determine the size and locations of flaws on the surface of the wafer. This provides a satisfactory pass/fail test for inspecting the wafers, however, the nature and source of the flaws are not suitably analyzed by such laser inspection techniques. Also, when the wafer has been etched with a pattern to form the microchips the etching may provide spurious indications of flaws on the surface.
To inspect the patterned surface of silicon wafers, low angle laser surface inspection devices are employed, such as those disclosed in Koizumi et al. U.S. Pat. No. 4,614,427 and Shiba et al. U.S. Pat. No. 4,669,875 for example. These devices inspect the surfaces of patterned wafers using a laser beam at a low glancing angle. However, laser scanning does not provide sufficient resolution or clarity of the flaws to analyze the nature or source of the flaws in the surface.
Optical scanning arrangements are known which use optical lenses to microscopically view the surface and identify and analyze flaws in the surface. However, such systems produce enormous amounts of data and require powerful computers to process and analyze the data produced. Accordingly such systems are very expensive. Because of the small field of view and the enormous volume of data obtained, this type of system is relatively slow.
In one recently developed device, Hitachi model HILIS-200, foreign particles are detected by a low angle fixed spot laser beam. As the wafer rotates and translates under the laser beam, the particles are detected by an overhead photomultiplier and a map of the particles is formed. Subsequently, the foreign particles may be microscopically observed and photographed by repositioning the flaw under a microscopic viewing device. However, this requires a very accurate and reliable X-Y table to reposition the flaws in the field of view. Also, the process of inspecting the wafers by moving the wafer around under the fixed spot laser is slow and time consuming.
Accordingly, it is an object of the present invention to provide a system for inspecting a surface which efficiently identifies and analyzes flaws and which avoids the limitations and disadvantages of the prior art as noted above.
It is a further object of the present invention to provide a system which quickly identifies flaws on the surface of an article and interactively analyzes the identified flaws.